1. Field of the Invention
The present invention relates to an alignment apparatus, and in particular, to an alignment apparatus, which prevents work from being damaged due to contact between the work and periphery edge of a table sucking the same, and is capable of detecting the position of the outer edge of the work with a high precision.
2. Related Art
Conventionally, the processing of work (semiconductor wafer (hereinafter, referred to as wafer)) includes, for example, a dicing process in which, after a circuit surface is formed on one side of a wafer, the wafer is cut into an appropriate chip size through various processes such that the rear surface thereof is polished with the circuit surface covered with a film, and the like.
In many processes as described above, an apparatus called wafer alignment apparatus (wafer positioning apparatus), of which object is to shift the center of wafer to a predetermined position and to align the chip alignment direction to a predetermined direction, is often incorporated into a variety of machines in the process.
In this apparatus, called aligner, a non-contact type, which does not come into mechanical contact with the most breakable wafer periphery edge, has become the main trend. The aligner is provided with such function that the central position and orientation of the wafer are obtained by performing calculation based on the wafer configuration characteristics and positional information obtained by an optical sensor and rotational and horizontal wafer shift means, and it is arranged so that the wafer is shifted to a predetermined position by the shift means.
More specifically, when a wafer is placed onto a generally flat wafer loading plane provided to a table by a transfer means such as a robot, the aligner turns the loading plane and wafer along with the table in a horizontal plane while sucking the wafer with a wafer suction means provided inside the wafer loading plane; a sensor head detects the periphery position of the wafer with respect to the rotational position of the table along with the position of an orientation mark indicating direction reference for chip alignment; and the wafer central position and the orientation mark are aligned to a predetermined position by rotating and shifting the table in X- and Y-directions in a horizontal plane based on the data output by the sensor, which outputs data for aligning the same, to the predetermined position; thus the wafer is made ready to be transferred to the next process.
The aligner is used in various machines such as a tester called prober, a wafer mounter which integrally attaches a ring frame and a wafer to each other with an adhesive film, and a dicing apparatus.
As for the type of the sensor head, in the case of an optical unit, of which sensor head comprises a light emitting side and a light receiving side, a transmission sensor system is often adopted in which a work is placed with its periphery portion being optically sandwiched by the light emitting side and the light receiving side, and the position of the periphery of the wafer is detected based on information of altered amount of the transmitted light.
In the above system, generally, it is arranged so that the periphery portion of the wafer is positioned outside the table being protruding in the air, and that the sensor head detects the position of the protruding portion. The aligner of this type is applicable with no problem to wafers of up to approximately 200 μm in thickness before dicing.
However, in these days, wafers are required to be extremely thin to 50 μm–200 μm in thickness. Owing to this, since polished wafer cannot maintain its plane configuration, in some cases, wafer periphery area protruding out of the table trails down due to its own weight. Consequently, in the alignment apparatus of conventional type, when the table is rotated, the wafer periphery area is apt to move up/down causing flip-flops by wind pressure due to the rotation. At this time, a large load is intensively applied to the contact position of the periphery area of the wafer with the periphery edge of the table due to the action of the principle of leverage having the fulcrum at the contact position and resulting in such problem that the surface of the wafer gets damaged. Such a problem occurs more frequently when the flip-flop is larger; i.e., when the rotation speed of the table is faster, or when the protruding width of the wafer is larger, resulting in such a problem that the setting of the rotation speed of the table and the size of the wafer are restricted. Further, due to the trail-down and flip-flop of the wafer, another problem occurs that the detection of the periphery position of the wafer becomes difficult, which decreases the detection accuracy by the sensor.